Electric typewriters generally include provisions for both single and repeat spacing and consequently there is a need for a device which will enable an operator to easily distinguish between actuation of the space bar for single spacing as opposed to repeat spacing. With the advent of ever increasing labor and material costs, this device must combine: ease of manufacture and assembly, for low initial cost, with high reliability and ease of maintenance for low cost of ownership. These requirements rule out the use of complex mechanisms which require close tolerances and careful adjustments during assembly.
The prior art related to electric typewriters includes examples of various devices for enabling an operator to distinguish between single and repeat spacing. Examples of such devices may be found in U.S. Pat. No. 2,896,767 to J. P. Barkdoll and U.S. Pat. No. 3,212,616 to L. P. Frechette et al. The devices shown in these patents are each characterized by the use of a first spring which resists the downward motion of a space bar, for single spacing, and a relatively complex linkage mechanism which incorporates a second spring for increased resistance to motion of the space bar, for repeat spacing. The disadvantages of these devices are directly related to their overall complexity and the relatively large number of component parts which are required for operation. The relatively large number of component parts results in a relatively high cost of ownership which is caused by the greater incidence of wear and fatigue problems on the various links, springs and pivots. The complexity of these devices makes it relatively difficult and costly to repair these devices and difficult even to perform routine maintenance adjustment and cleaning operations.